As a process for commercially producing polymers such as polycarbonate, polyarylate and polyester polycarbonate, an interfacial polycondensation method is preferably employed.
In the interfacial polycondensation method, for example, of polycarbonate, an emulsion solution obtained after completion of the reaction is subjected to a washing and separation operation to obtain a methylene chloride solution of polycarbonate. Thereafter, from the methylene chloride solution of polycarbonate (PCM), polycarbonate is isolated to produce the polycarbonate.
As a method of isolating polycarbonate from the methylene chloride solution of polycarbonate, various ones are under investigation.
For example, a method of adding a poor solvent to the solution of polycarbonate (Japanese Patent Publication No. 4474/1967), a grinding method with a kneader, utilizing crystallization of a polycarbonate solution (Japanese Patent Publication No. 15899/1987), a method of throwing into hot water (Japanese Patent Application Laid-Open No. 115625/1985), and so forth are known.
All of these methods, however, are increased in plant cost, as a method of isolating polymers such as polycarbonate, and thus have a problem in respect of cost. Therefor in order to decrease the cost, a more simplified isolating method is desired.
As methods for solving the problems, improved techniques are disclosed in Japanese Patent Publication No. 54329/1985 and Japanese Patent Publication No. 45648/1990.
In any of the methods disclosed therein, however, steam or nitrogen gas, etc. are needed for evaporation of methylene chloride as the solvent, and they still have a problem of recovery of removed solvent. Furthermore they have problems that only polymer particles having large particle diameters are obtained, and large equipment and a lot of energy are needed for removal of the solvent. Furthermore they have problems that water accumulates in the system, which will need an operation to withdraw the water, and at the same time, polymers obtained contain a large amount of water.